Remove deprecated code for the 2.0 release

dense-analysis#1621 - Tolerate SetOptions calls when ALE is loaded in…

… a weird way

Mention g:ale_linters_explicit in the README

Revert "Merge pull request dense-analysis#1487 from rhysd/fix-1472"

This reverts commit 67b7165.

Fix dense-analysis#1404 - Do not show balloons when g:ale_set_balloon…

…s is 0. Add b:ale_set_balloons

Fix dense-analysis#1298 - Escape commands for PowerShell

Fix the mscs tests on Windows, and use the improved Simplify for all …

…tests instead.

Stop the completion tests from failing randomly

Fix dense-analysis#1101 - Ignore no-implicit-dependencies errors unti…

…l TSLint supports checking via stdin properly

Add a badge for AppVeyor, and remove some trailing spaces from the RE…

…ADME